Mast for loop direction finding system



Nov. 12, 1968 E. A. MEYERS. JR

MAST FOR LOOP DIRECTION FINDING Filed Nov. 5, 1965 ll IIIllllllllllllalllllllll'll .vv. PWwuF: 5% @Br m INVENT ELMER A\M Y RS I d- 'W, M Z.

ATTORNEYS United States Patent 3,411,111 MAST FOR LOOP DIRECTION FINDING SYSTEM Elmer A. Meyers, Jr., Cupertino, Calif., assignor by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Nov. 5, 1965, Ser. No. 506,920 6 Claims. (Cl. 33312) This invention relates to a mast for a loop direction finding antenna and more particularly to a mast having a ferrite choke therein to prevent undesirable oscillations from occurring in the mast.

In the operation of a direction finding antenna, sence information is obtained by adding the signals from a loop antenna and a monopole antenna after one of them has been shifted ninety degrees in phase. Phase shifts in the monopole signal due to changes in the height of the antenna above ground and various ground conditions can completely destroy the sense information or cause it to be erroneous. The height above ground problem is due primarily to different modes of oscillation in the mast or mast structure wavelength resonances). Since the antenna head supported by the mast contains a preamplifier, power and control wires, a coaxial cable must necessarily be strung through the mast. Therefore, resonances will occur with both dielectric and metal masts.

In the system in which this new mast is used some means for preserving the sense information is necessary. One method for preserving-this information is to mount a ground plane below the monopole antenna. The ground plane establishes a ground reference for the monopole and is a solution to the problem. However, it is not a very practical solution since the ground plane assembly is unwieldly to rotate and does not lend itself to portable operation. The structure described herein is an excellent solution to the problem of preserving sense information as it allows the desired performance of the system to be obtained without the use of a cumbersome ground plane.

The solution to the above mentioned problem is obtained by lowering the Q of the mast structure. This is accomplished by fabricating the mast wiring into a cable which is covered with a shield braid on which a ferrite coaxial choke in connected.

An object of the present invention is to provide a mast for a direction finding antenna including a ferrite choke for preventing undesirable resonances in the mast structure and thereby preserving the sense information obtained by said direction finding antenna.

The nature of the present invention along with various advantages, objects and features thereof will become more apparent upon consideration of the accompanying drawings and the following detailed description of those drawings.

In the drawings:

FIGURE 1 is a cut-away view of the mast showing the wiring and choke therein, and

FIGURE 2 shows a particular choke which may be used in the mast.

Referring to FIGURE 1 there is shown a mast 11 which may be made from fiber glass tubing. The mast wiring is fabricated into a cable 12 which is covered with shield braid 13 which connects to a connector 14 at the top of the mast to provide complete shielding. A similar connector (not shown) is attached to the braid 13 at the bottom of the mast.

A coaxial ferrite choke 15 is supported within the mast tubing by four plastic foam supports 16. The ferrite choke is insulated from the shield braid along the entire length of the choke except at its upper end where the braid and the choke are conductively connected together by solder 17. The insulation is provided by wrapping plastic insulative tape 18 around the shield braid throughout the length of the choke.

FIGURE 2 shows the construction of a preferred embodiment of the ferrite choke 15. The ferrite cylinder shown in FIGURE 2 comprises a stack of doughnutshaped ferrite rings 21 around which is wrapped a sheet of brass 22 (see FIG. 1). Brass discs 23 and 24 are soldered to the top and bottom of the ferrite cylinder.

The overall dimensions of the choke are related to the type of material used and the frequency of operation; the optimum size can be determined by a cut and try procedure. A lossy ferrite material is used, tending to lower the Q of the mast structure and provide broad band operation.

What is claimed is:

1. A mast for a direction finding antenna comprising: an elongated tubular mast; a shielded cable extending throughout the entire length of said tubular mast; a hollow ferrite cylinder supported within said tubular mast, said cable passing through the hollow portion of said ferrite cylinder; means for insulating said cable from said ferrite cylinder throughout the length of said ferrite cylinder except at the extreme top end thereof; means for conductively connecting the extreme top end of said ferrite cylinder to said cable; a thin conductive cylinder surrounding the outer portion of said ferrite cylinder and two conductive discs, one conductively joined to each end of said cylinder and to said conductive cylinder.

2. A mast as set forth in claim 1 in which said ferrite cylinder comprises a plurality of doughnut-shaped ferrite rings.

3. A mast as set forth in claim 1 wherein said insulating means consists of insulative tape wrapped around said cable.

4. A mast for a direction finding antenna comprising: an elongated tubular mast; a ferrite cylinder supported within said mast by a plurality of elongated plastic foam sections, said cylinder having an axial hole therein and a metallic covering on the outer surface and the two end surfaces thereof; a shielded cable extending through said mast and through the hole in said cylinder, the portion of said cable within said cylinder having an insulative cov-' ering; and means for conductively connecting the end of said ferrite cylinder which is located in the uppermost part of said mast to said cable.

5. A mast as set forth in claim 4 in which said tubular mast is made of fiber glass.

6. A mast as set forth in claim 5 which further includes an electrical connector attached to each end of said cable.

References Cited UNITED STATES PATENTS 2,111,651 3/1938 Wentz 33312 2,322,971 6/1943 Roosenstein 33312 2,419,855 4/ 1947 Roosenstein 33312 2,524,857 10/ 1950 Secker 33381 2,669,695 2/1954 Bird 33312 3,035,237 5/1962 Schlicke 33379 3,380,004 4/ 1968 Hansen 33379 FOREIGN PATENTS 603,1 19 6/1948 Great Britain. 887,578 1/ 1962 Great Britain.

ELI LIEBERMAN, Primary Examiner. W. H. PUNTER, Assistant Examiner. 

1. A MAST FOR A DIRECTION FINDING ANTENNA COMPRISING: AN ELONGATED TUBULAR MAST; A SHIELDED CABLE EXTENDING THROUGHOUT THE ENTIRE LENGTH OF SAID TUBULAR MAST; A HOLLOW FERRITE CYLINDER SUPPORTED WITHIN SAID TUBULAR MAST, SAID CABLE PASSING THROUGH THE HOLLOW PORTION OF SAID FERRITE CYLINDER; MEANS FOR INSULATING SAID CABLE FROM SAID FERRITE CYLINDER THROUGHOUT THE LENGTH OF SAID FERRITE CYLINDER EXCEPT AT THE EXTREME TOP END THEREOF; MEANS FOR CONDUC- 